The present invention relates to a support device for securing workpieces.
In particular, the invention relates to a device mounted on equipment designed to secure both curved and flat pieces of sheet material, typically body pressings or fuselage panels or the like, during the course of machining operations performed on these same pieces.
In sectors such as the aerospace and shipbuilding industries, machining cycles need to be carried out on pieces very often of appreciable dimensions and of curved and irregular geometry, a fact that both complicates the handling of such items considerably and causes notable difficulty in making the work secure during machining operations.
To optimize the positioning of these large items, installations typical of the prior art employ a rigid frame or gantry carrying a unit by which the work is machined. The workpiece is placed beneath the frame, and to achieve stable positioning, such installations comprise a plurality of columns, each equipped at its free top end with a support device, to which the parts for machining can be securely anchored; this ensures that machining distances are accurately maintained and that machining tools will encounter a suitably firm reaction force.
The supporting columns are capable of vertical movement, so as to adapt to the dissimilar heights that different parts of the workpiece may occupy by reason of its curved geometry.
Moreover, the curved or at all events irregular profile of the workpiece dictates also that the support devices fitted to the columns should be capable of adapting to the angle of inclination presented by the piece at the point of engagement with each device.
Conventional support devices normally comprise an aspirating element, typically a suction cup, and a ball and socket structure to which the aspirating element is mounted.
Patent EP 69230, by way of example, discloses a positioning and holding device that comprises a plenum chamber in the form of a spherical shell, surrounded uppermost by a sealing rim positioned to engage in contact with the workpiece.
During the positioning step, overpressure is generated in the hemispherical chamber of the aspirating element so that the workpiece is carried on an air cushion, and can be maneuvered while floating substantially free of frictional contact.
The spherical shell rests on a cup, likewise of essentially spherical geometry, and can be shifted through predetermined angles relative to this same cup so as to adapt to the angle of inclination of the workpiece being supported.
Numerous other solutions exist for such support devices, comprising elements that appear spherical or in any event are positionable by means of a ball joint type mechanism.
The solutions in question have proved effective to a degree, but are not without drawbacks.
A first drawback consists in the fact that chips and dust can easily be deposited on and penetrate the ball joints during the course of machining operations. This is a situation that can impede the movement of the elements making up the support devices and even cause them to seize, in extreme cases, with a self-evidently negative impact on the duration and precision of the machining operations that need to be carried out.
To the end of avoiding the drawbacks in question, and ensuring that dust and machining debris will not affect the effectiveness of the ball joints, lengthy and thorough cleaning operations must be carried out between one machining cycle and the next, or even while machining is in progress.
Another drawback connected with the use of ball joints in support devices of the type in question is that of the limited angle of maneuver afforded to the component parts of the joint, and therefore to the suction cup directly engaging the workpiece.
With this in mind, patent EP 507033, for example, discloses a device comprising a ball joint with an intermediate shell designed to increase the angle of inclination that can be accommodated.
Whilst the addition of an intermediate spherical shell represents a positive step, on the one hand, in that it provides the suction cup with increased freedom of angular movement, it serves on the other only to enlarge the areas of the joint exposed to the risk of penetration by machining debris, chips or dust as mentioned above.
Accordingly, the object of the present invention is to provide a support device for securing workpieces that will be unaffected by the drawbacks mentioned above, and moreover will be practical and effective in use.